Androgens play important roles in post-natal development that are most pronounced at adrenarche and pubarche. Androgen production promotes the musculoskeletal anabolism associated with the pubertal growth in both males and females. At puberty, ovarian and testicular androgens are responsible for pubertal hair, acne, and enhancement of libido. In males, exposure to 100-fold increased levels of endogenous androgens results in the gender dimorphism in bone mass, muscle mass (positive nitrogen balance), and upper body strength, and are required for normal sexual development (genitalia, spermatogenesis, prostate and seminal vesicle maturation). Delay in puberty decreases the peak bone mass achieved during adulthood. (Bhasin, S., et al., Eds. Pharmacology, Biology, and Clinical Applications of Androgens: Current Status and Future Prospects. Wiley-Liss, Inc.: New York, 1996). In women, natural menopause causes virtually complete loss of ovarian estrogen production and gradually reduces ovarian production of androgen by approximately 50%. The physiological consequences of reduced androgen production after menopause are evident in decreased energy and libido, and contribute significantly in many women to vasomotor symptoms. Decreased androgen output is also thought to contribute—along with declining pituitary growth hormone (GH) secretion and insulin derived growth factor 1 (IGF1) action—to age-dependent sarcopenia, negative nitrogen balance and loss of bone mass. (Vestergaard, et al., Effect of sex hormone replacement on the insulin-like growth factor system and bone mineral: a cross-sectional and longitudinal study in 595 perimenopausal women participating in the Danish Osteoporosis Prevention Study, J Clin Endocrinol Metab. 84:2286–90, 1999; and Bhasin, et al., Eds. Pharmacology, Biology, and Clinical Applications of Androgens: Current Status and Future Prospects, Wiley-Liss, Inc.: New York. 1996). Postmenopausal osteoporosis results mainly from estrogen deficiency. However, many women who received estrogen replacement therapy still lose bone with age and develop age-related osteoporotic fractures (albeit at a lower rate than those taking estrogens), indicating that both estrogens and androgens play important roles for bone health in both women and men. The simultaneous decreases in bone mass, muscle mass and muscle strength increase the risk of falls and especially of hip fractures in both men and women >65 years of age. In fact, one-third of all hip fractures occur in men.
The androgen receptor (AR) belongs to the nuclear receptor superfamily and controls transcription in a ligand dependent manner (Brinkman, et al., Mechanisms of androgen receptor activation and function, J. Ster. Biochem. Mol. Biol. 69, 307–313, 1999). Upon androgen binding, AR binds directly to specific DNA sequences present in the promoter region of androgen responsive genes, termed androgen response elements (AREs), to stimulate transcription. Ligands that interact witht the AR and activate or repress gene transcription are classified as AR agonists, whereas ligands that interact with AR and block transactivation or transrepression of genes induced by endogenous androgens are classified as AR antagonists. A number of natural or synthetic androgen agonists have been used for treatment of musculoskeletal or hematopoietic disorders and for hormone replacement therapy. In addition, AR antagonists, such as flutamide or bicalutamide, are used for treatment of prostate cancer. However, clinical use of these androgen agonists or antagonists have been limited because of undesirable effects, such as hirsutism and prostate enlargement for agonists, and bone loss, fracture, gynecomastia and sarcopenia for antagonists. It would be useful to have available androgens with tissue selective agonistic activity, which increase bone formation and muscle mass but do not induce the virilization.
Osteoporosis is characterized by bone loss, resulting from an imbalance between bone resorption (destruction) and bone formation, which starts in the fourth decade continues throughout life at the rate of about 1–4% per year (Eastell, Treatment of postmenopausal osteoporosis, New Eng. J. Med. 338: 736, 1998). In the United States, there are currently about 20 million people with detectable fractures of the vertebrae due to osteoporosis. In addition, there are about 250,000 hip fractures per year due to osteoporosis, associated with a 12%–20% mortality rate within the first two years, while 30% of patients require nursing home care after the fracture and many never become fully ambulatory again. In postmenopausal women, estrogen deficiency leads to increased bone resorption resulting in bone loss in the vertebrae of around 5% per year, immediately following menopause. Thus, first line treatment/prevention of this condition is inhibition of bone resorption by bisphosphonates, estrogens, selective estrogen receptor modulators (SERMs) and calcitonin. However, inhibitors of bone resorption are not sufficient to restore bone mass for patients who have already lost a significant amount of bone. The increase in spinal BMD attained by bisphosphonate treatment can reach 11% after 7 years of treatment with alendronate. In addition, as the rate of bone turnover differs from site to site; higher in the trabecular bone of the vertebrae than in the cortex of the long bones, the bone resorption inhibitors are less effective in increasing hip BMD and preventing hip fracture. Therefore, osteoanabolic agents, which increase cortical/periosteal bone formation and bone mass of long bones, would address an unmet need in the treatment of osteoporosis especially for patients with high risk of hip fractures. The osteoanabolic agents also complement the bone resorption inhibitors that target the trabecular envelope, leading to a biomechanically favorable bone structure. (Schmidt, et al., Anabolic steroid: Steroid effects on bone in women, 1996, In: J. P. Bilezikian, et al., Ed. Principles of Bone Biology. San Diego: Academic Press.)
A number of studies provide the proof of principle that androgens are osteoanabolic in women and men. Anabolic steroids, such as nandrolone decanoate or stanozolol, have been shown to increase bone mass in postmenopausal women. Beneficial effects of androgens on bone in post-menopausal osteoporosis are well-documented in recent studies using combined testosterone and estrogen administration (Hofbauer, et al., Androgen effects on bone metabolism: recent progress and controversies, Eur. J. Endocrinol. 140, 271–286, 1999). Combined treatment increased significantly the rate and extent of the rise in BMD (lumbar and hip), relative to treatment with estrogen alone. Additionally, estrogen—progestin combinations that incorporate an androgenic progestin (norethindrone) rather than medroxyprogesterone acetate yielded greater improvements in hip BMD. These results have recently been confirmed in a larger (N=311) 2 year, double blind comparison study in which oral conjugated estrogen (CEE) and methyltestosterone combinations were demonstrated to be effective in promoting accrual of bone mass in the spine and hip, while conjugated estrogen therapy alone prevented bone loss (A two-year, double-blind comparison of estrogen-androgen and conjugated estrogens in surgically menopausal women: Effects on bone mineral density, symptoms and lipid profiles. J Reprod Med. 44(12):1012–20, 1999). Despite the beneficial effects of androgens in postmenopausal women, the use of androgens has been limited because of the undesirable virilizing and metabolic action of androgens. The data from Watts and colleagues demonstrate that hot flushes decrease in women treated with CEE+methyltestosterone; however, 30% of these women suffered from significant increases in acne and facial hair, a complication of all current androgen pharmacotherapies (Watts, et al., Comparison of oral estrogens and estrogens plus androgen on bone mineral density, menopausal symptoms, and lipid-lipoprotein profiles in surgical menopause, Obstet. Gynecol. 85, 529–537, 1995). Moreover, the addition of methyltestosterone to CEE markedly decreased HDL levels, as seen in other studies. Thus, the current virilizing and metabolic side effect profile of androgen therapies provide a strong rationale for developing tissue selective androgen agonists for bone.
It is well established that androgens play an important role in bone metabolism in men, which parallels the role of estrogens in women. (Anderson, et al., Androgen supplementation in eugonadal men with osteoporosis—effects of 6 months of treatment on bone mineral density and cardiovascular risk factors, Bone 18: 171–177, 1996). Even in eugonadal men with established osteoporosis, the therapeutic response to testosterone treatment provides additional evidence that androgens exert important osteoanabolic effects. Mean lumbar BMD increased from 0.799 gm/cm2 to 0.839 g/cm2, in 5 to 6 months in response to 250 mg of testosterone ester IM q fortnight (p=0.001). A common scenario for androgen deficiency occurs in men with stage D prostate cancer (metastatic) who undergo androgen deprivation therapy (ADT). Endocrine orchiectomy is achieved by long acting GnRH agonists, while androgen receptor blockade is implemented with flutamide or bicalutamide (AR antagonists). In response to hormonal deprivation, these men suffer from hot flushes, significant bone loss, weakness, and fatigue. In a recent pilot study of men with stage D prostate cancer, osteopenia (50% vs. 38%) and osteoporosis (38% vs. 25%) were more common in men who had undergone ADT for >1 yr than the patients who did not undergo ADT (Wei, et al. Androgen deprivation therapy for prostate cancer results in significant loss of bone density, Urology 54: 607–11, 1999). Lumbar spine BMD was significantly lower in men who had undergone ADT (P=0.008). Thus, in addition to the use of tissue selective AR agonists for osteoporosis, tissue selective AR antagonists in the prostate that lack antagonistic action in bone and muscle may be a useful treatment for prostate cancer, either alone or as an adjunct to traditional ADT such as GnRH agonist/antagonist. (See also Stoche, et al., J Clin. Endocrin. Metab. 86:2787–91, 2001).
Additionally, it has been reported that patients with pancreatic cancer treated with the antiandrogen flutamide have been found to have increased survival time. (Greenway, B. A., Drugs & Aging, 17(3), 161, 2000). The tissue selective androgen receptor modulators of the present invention may be employed for treatment of pancreatic cancer, either alone or as an adjunct to treatment with an antiandrogen.
The possibility of tissue selective AR agonism was suggested by androgen insensitivity syndrome (AIS), which results from mutations in AR gene located at X chromosome. (Quigley, et al., Androgen receptor defects: Historical, clinical, and molecular perspectives. Endocrine Reviews. 16:546–546, 1995). These mutations cause different degrees of androgen insensitivity. While complete lack of androgen responsiveness develops as a female phenotype with female-type bones, subtle mutations (one amino acid substitution) of AR may lead to partial AIS with different degrees of abnormality in male sexual development often with male-type skeleton. A similar aberration in male sex organ development is also found in individuals with mutations in 5α-reductase type 2 gene, that converts testosterone to 5α-dihydro-testosterone (5α-DHT) (Mendonca, et al., Male pseudohermaphroditism due to steroid 5alpha-reductase 2 deficiency: Diagnosis, psychological evaluation, and management, Medicine (Baltimore), 75:64–76 (1996)). These patients exhibit partial development of male organs with normal male skeleton, indicating that testosterone cannot substitute for 5α-DHT as an activator of AR in genital development. This ligand specificity for certain tissues raises the possibility that androgenic compounds with AR agonistic activity could have specificity for certain tissues, such as bone, while lacking activity in other tissues, such as those responsible for virilization.
Recent advances in the steroid hormone receptor field uncovered the complex nature of transcription controlled by AR and other nuclear receptors (Brinkman, et al., Mechanisms of androgen receptor activation and function, J. Ster. Biochem. Mol. Biol. 69:307–313 1999). Upon binding to ARE as a homo-dimer, agonist-bound AR stimulates transcription by recruiting a large enzymatic co-activator complex that includes GRIP1/TIF2, CBP/p300 and other coactivators. Transcriptional activities of AR have been functionally mapped to both the N-terminal domain (NTD) and C-terminal ligand binding domain (LBD), also termed activation function AF1 and AF2, respectively. A feature of AR is the ligand mediated interaction of AR NTD with LBD (N-C interaction) which is essential for most ligand induced transcriptional activation. In addition, agonist-bound AR can also suppress transcription via protein-protein interaction with transcription factor complexes such as AP1, NFκB and Ets family. Both AR agonist-induced transcriptional activation and repression are context (cell type and promoter) dependent and are reversed by AR antagonists, providing the possibility for ligand-dependent, context specific agonism/antagonism. Androgenic ligands, thus, may lead to tissue selective AR agonism or partial AR agonism/antagonism, and have been named selective AR modulators (SARMs).
What is needed in the art are compounds that can produce the same positive responses as androgen replacement therapy without the undesired side effects. Also needed are androgenic compounds that exert selective effects on different tissues of the body. In this invention, we developed a method to identify SARMs using a series of in vitro cell-assays that profiles ligand mediated activation of AR, such as (i) N-C interaction, (ii) transcriptional repression, (iii) transcriptional activation dependent on AF1 or AF2 or native form of AR. SARM compounds in this invention, identified with the methods listed above, exhibit tissue selective AR agonism in vivo, i.e. agonism in bone (stimulation of bone formation in rodent model of osteoporosis) and antagonism in prostate (minimal effects on prostate growth in castrated rodents and antagonism of prostate growth induced by AR agonists). Such compounds are ideal for treatment of osteoporosis in women and men as a monotherapy or in combination with inhibitors of bone resorption, such as bisphosphonates, estrogens, SERMs, cathepsin K inhibitors, αVβ3 antagonists, calcitonin, proton pump inhibitors. SARM compounds may also be employed for treatment of prostate disease, such as prostate cancer and benign prostate hyperplasia (BPH). Moreover, compounds in this invention exhibit minimal effects on skin (acne and facial hair growth) and can be used for treatment of hirsutism. Additionally, compounds in this invention can exhibit muscle growth and can be used for treatment of sarcopenia and frailty. Moreover, compounds in this invention can exhibit androgen agonism in the central nervous system and can be used to treat vasomotor symptoms (hot flush) and can increase energy and libido, particularly in post-menopausal women. The compounds of the present invention may also be used in particular to treat female sexual dysfunction. The compounds of the present invention may be used in the treatment of prostate cancer, either alone or as an adjunct to traditional GnRH agonist/antagonist therapy for their ability to restore bone, or as a replacement for antiandrogen therapy because of the ability to antagonize androgen in the prostate, and minimize bone depletion in the skeletal system. Further, the compounds of the present invention may be used for their ability to restore bone in the treatment of pancreatic cancer as an adjunct to treatment with antiandrogen, or as solo agents for their antiandrogenic properties, offering the advantage over traditional antiandrogens of being bone-sparing. Additionally, compounds in this invention can increase the number of blood cells, such as red blood cells and platelets and can be used for treatment of hematopoietic disorders such as aplastic anemia. Finally, compounds in this invention have minimal effects on lipid metabolism, thus considering their tissue selective androgen agonism listed above, the compounds in this invention are ideal for hormone replacement therapy in hypogonadic (androgen deficient) men.
EP 1 002 799 assigned to Pfizer describes an optically pure androgen mediator of structural formula:
for use in the prevention and restoration of age-related decline in muscle mass and strength and the treatment of conditions which present with low bone mass in mammals, including humans.
U.S. Pat. No. 6,017,924, assigned to Ligand Pharmaceuticals, Inc., claims a compound of structural formula:
and its use as an androgen receptor modulator.
U.S. Pat. No. 5,688,808, assigned to Ligand Pharmaceuticals, Inc., claims compounds of structural formula:
as steroid receptor modulator compounds.
U.S. Pat. No. 5,696,130, assigned to Ligand Pharmaceuticals, Inc., claims compounds of structural formulae:
as high affinity, high selectivity modulators for steroid receptors. U.S. Pat. No. 6,093,821 is a divisional of U.S. Pat. No. 5,696,130, and claims a method for producing 6-substituted-1,2-dihydro N-1 protected quinolines.
PCT publication WO 01/16133, assigned to Ligand Pharmaceuticals, Inc., describes 8-substituted-6-trifluoromethyl-9-pyrido[3,2,-g]quinoline compounds of structural formulae:
as androgen receptor modulators.
PCT publication WO 01/16139 assigned to Ligand Pharmaceuticals, Inc., describes compounds of structural formulae:
as agonists, partial agonists and antagonists for the androgen receptor.